In Vitro Antimicrobial Efficacy of MTAD and Sodium Hypochlorite

Entire study published in the Journal of Endodontics
Vol. 29, No. 7, July 2003
Shahrokh Shabahang, DDS, MS, PhD, Manouchehr Pouresmail, DMD, and Mahmoud Torabinejad, DMD, MSD, PhD

Overview:
Studies have shown that bacteria are essential for the development of pulpal and periradicular diseases. The main objectives of root canal therapy are removal of diseased tissue, elimination of microorganisms present in the canals and dentinal tubules, and prevention of recontamination after treatment. Current techniques of root canal debridement leave many areas of the root canal system (RCS) completely untouched by the instruments. Thus, a root canal irrigant is needed to aid in the debridement of the canals.

A number of factors may present obstacles in achieving complete disinfection of the RCS. The root canal morphology in human teeth is complex and contains many fins, culs-de-sac, lateral canals, and dental tubules. Bacteria may be present not only in these irregularities but also in the dentinal tubules at varying depths. The cutting action of the instruments creates a smear layer that can prevent penetration of disinfecting solutions into the tubules. Furthermore, the smear layer itself may contain bacteria, and it may aid in the adherence of the microorganisms to the root canal walls.

Sodium hypochlorite (NaOCl) is currently a commonly used root canal irrigant. Aside from its unpleasant odor and taste, NaOCl has several limitations. It does not consistently disinfect the RCS, and it does not remove the smear layer from dentin walls. In addition, it is very toxic when it is extruded into the periradicular tissues.

Purpose:
The purpose of this study was to compare the ability of MTAD with that of NaOCl to disinfect human root canals that had been contaminated with whole saliva.

Materials and Methods:
One hundred and thirty-two root canals of extracted human teeth were cleaned and shaped using the passive step-back technique and rotary NiTi files. The smear layer was removed, and the teeth were autoclaved.

Six autoclaved samples were transferred to sterile broth without contamination with saliva to serve as negative controls. Whole saliva was used to contaminate the root canals of the rest of the samples for 48 hours. Six of these contaminated samples were irrigated with Brain Heart Infusion (BHI) broth and served as positive controls. The rest of the contaminated specimens were then divided into two experimental groups of 60 teeth each. In one group, the canals were irrigated with 1 ml MTAD, and the samples were immersed in 2 ml of the same solution for 5 minutes. In the second group, the specimens were similarly treated with 5.25% NaOCl. All samples were washed in BHI broth and then placed in another tube containing BHI broth and incubated for 96 hours. Disinfection of the samples was determined based on presence or absence of turbidity in the broth 96 hours later.

Conclusion:
 
Table 1. Comparison of the antimicrobial effect of MTAD and NaOCl after a 5-minute exposure of saliva-contaminated roots to the irrigants.

Exposure Time	Sample Size	Growth	No Growth
Negative controls	6	0	6
Positive controls	6	6	0
MTAD	60	1	59
NaOCl	60	23	37

All of the positive control samples showed signs of turbidity, whereas none of the negative controls showed turbidity. Table 1 shows the tabulated results of the experiment. Twenty-three of the 60 samples treated with 5.25% NaOCl remained contaminated, as evidenced by turbidity of the BHI broth after 96 hours. In contrast, all but one of the 60 samples treated with MTAD were completely sterile as evidenced by lack of turbidity of the broth. There was a significant difference between samples treated with MTAD and those treated with 5.25% NaOCl (p < 0.0001).

The results of the investigation confirmed previous findings demonstrating almost 40% of the root canals remain infected using NaOCl and the superior antimicrobial activity of MTAD when compared with 5.25% NaOCl. An important finding in the study was the ability of MTAD to exert its antimicrobial effect during a brief time. This property is desirable in clinical practice where the root canal irrigants may be in contact with certain areas of the RCS for a short time. Furthermore, this disinfecting property obviates the need for placement of an intracanal dressing necessitating multiple visits.